From fecd704833b996e02b8029235a5d0a25a85a28e5 Mon Sep 17 00:00:00 2001
From: Artem Senichev <artemsen@gmail.com>
Date: Sun, 15 Sep 2024 11:12:21 +0300
Subject: [PATCH] Fix multithreading drawing

Handles the first task in the current thread.

Signed-off-by: Artem Senichev <artemsen@gmail.com>
---
 src/pixmap.c | 30 ++++++++++++++++++++++++------
 src/ui.c     |  7 +++----
 2 files changed, 27 insertions(+), 10 deletions(-)

diff --git a/src/pixmap.c b/src/pixmap.c
index 008df57..0aa2f1f 100644
--- a/src/pixmap.c
+++ b/src/pixmap.c
@@ -445,9 +445,13 @@ void pixmap_scale(enum pixmap_scale scaler, const struct pixmap* src,
     const long cpus = sysconf(_SC_NPROCESSORS_ONLN);
 #endif
 
-    const size_t threads_num = cpus > 0 ? min(16, cpus) : 1;
-    struct scale_task* tasks = malloc(threads_num * sizeof(struct scale_task));
-    scale_fn fn = scaler == pixmap_nearest ? scale_nearest : scale_bicubic;
+    // background threads
+    const size_t threads_num = min(16, max(cpus, 1)) - 1;
+    struct scale_task* tasks = NULL;
+
+    const scale_fn scaler_fn =
+        scaler == pixmap_nearest ? scale_nearest : scale_bicubic;
+
     struct scale_param sp = {
         .src = src,
         .dst = dst,
@@ -457,15 +461,29 @@ void pixmap_scale(enum pixmap_scale scaler, const struct pixmap* src,
         .alpha = alpha,
     };
 
+    // create task for each CPU core
+    if (threads_num) {
+        tasks = malloc(threads_num * sizeof(struct scale_task));
+        if (!tasks) {
+            return;
+        }
+    }
+
+    // start background threads
     for (size_t i = 0; i < threads_num; ++i) {
         struct scale_task* task = &tasks[i];
+        task->tid = 0;
         task->sp = &sp;
-        task->start = i;
-        task->step = threads_num;
-        task->fn = fn;
+        task->start = i + 1; // skip first line
+        task->step = threads_num + 1;
+        task->fn = scaler_fn;
         pthread_create(&task->tid, NULL, scale_thread, task);
     }
 
+    // execute the first task in the current thread
+    scaler_fn(&sp, 0, threads_num + 1);
+
+    // wait for all threads to complete
     for (size_t i = 0; i < threads_num; ++i) {
         pthread_join(tasks[i].tid, NULL);
     }
diff --git a/src/ui.c b/src/ui.c
index 9f6b77b..b6e0f41 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -751,10 +751,9 @@ void ui_draw_commit(void)
 #ifdef TRACE_DRAW_TIME
     struct timespec curr;
     clock_gettime(CLOCK_MONOTONIC, &curr);
-    printf("%ld ms\n",
-           (curr.tv_sec * 1000 + curr.tv_nsec / 1000000) -
-               (ctx.wnd.draw_time.tv_sec * 1000 +
-                ctx.wnd.draw_time.tv_nsec / 1000000));
+    const double ns = (curr.tv_sec * 1000000000 + curr.tv_nsec) -
+        (ctx.wnd.draw_time.tv_sec * 1000000000 + ctx.wnd.draw_time.tv_nsec);
+    printf("Rendered in %.6f sec\n", ns / 1000000000);
 #endif
 
     wl_surface_attach(ctx.wl.surface, ctx.wnd.current, 0, 0);